As mentioned earlier, DMA maps represent memory areas (that is to say, DMA segments) that have been allocated according to the properties of a DMA tag and are within device visible address space.

DMA maps can be managed with the following functions:

#include <machine/bus.h>

int
bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp);

int
bus_dmamap_destroy(bus_dma_tag_t dmat, bus_dmamap_t map);

The bus_dmamap_create function creates a DMA map based on the DMA tag dmat and stores the result in mapp. The flags argument modifies bus_dmamap_create’s behavior. Table 12-2 displays its only valid value.